The eye is fundamentally one of the most important organs during life. Because of aging, diseases and other factors which can adversely affect vision, the ability to maintain the health of the eye becomes all important. A leading cause of blindness is the inability to introduce drugs or therapeutic agents into the eye and maintain these drugs or agents at a therapeutically effective concentration therein. Oral ingestion of a drug or injection of a drug at a site other than the eye provides the drug systemically. However, such systemic administration does not provide effective levels of the drug specifically to the eye and thus may necessitate administration of often unacceptably high levels of the agent in order to achieve effective intraocular concentrations. On the other hand, when a drug is injected into the eye, it quickly washes out or is depleted from within the eye into the general circulation. From the therapeutic standpoint, this may be as effective as giving no drug at all. Because of these inherent difficulties of delivering drugs into the eye, present medical treatments of ocular diseases are inadequate.
The need for a solution to these difficulties in ocular therapy is even more pressing in that a number of ocular diseases have now been identified, many of which are amenable to treatment if a proper mode of therapeutic delivery is available. It is therefore of great interest to develop modes of treatment which obviate the limitations of present modes of therapy.